This invention relates to shear valves primarily intended for use with fuel delivery systems, including petrol and liquefied petroleum gas (LPG).
There is a concern that fuel delivery systems in fuel filling stations should be provided with connection to the liquid fuel line which, if damaged, e.g. by impact from a road vehicle, will break in such a way as to shut off the fuel connections so as to minimise leakage of fuel in such an incident onto the forecourt of the filling station.
In some fuel filling stations, fuel is dispensed from tanks in which the fuel delivery pump is submerged in the tank. As a consequence, accidental damage to the fuel delivery pedestal during dispensing of fuel can result in fuel being pumped onto the forecourt from a fractured delivery pipe.
This invention particularly relates to the provision of arrangements for overcoming the above problems.
According to one aspect of the present invention there is provided a shear valve for use in a fuel delivery system which comprises a valve body wherein a first end is adapted to be connected to a fuel inlet and a second oppositely disposed end is adapted to be connected to a fuel outlet, said first end including an emergency shut-off valve which is biased towards its closed position, and the valve body having a readily frangible or separable region between said ends and said emergency shut-off valve normally being held open by a displaceable abutment comprising at least one ball or roller.
Preferably, the second end houses a non-return valve which is arranged to prevent fuel from flowing out of the damaged or fractured valve body from the fuel delivery end.
In one embodiment, the displacement abutment comprises one or more rollers or balls, the arrangement being such that distortion or breakage of the valve body causes displacement of a roller and/or ball, with resulting closure of the shut-off valve.
In a preferred embodiment, the displaceable abutment comprises a ball or roller which is normally held in place by engagement with a pointed member, the arrangement being such that distortion or breakage of the valve body causes relative movement of the ball or roller or the pointed member, with resulting closure of the shut-off valve. A ball is preferred because it takes up less space and alignment with the pointed member and an operating portion of the shut-off valve is easier to achieve. The term xe2x80x9cpointed memberxe2x80x9d is intended to include any tapered member. For example, it may be cone or wedge shaped and may have a blunt or sharp tip. In this context, xe2x80x98conexe2x80x99 includes members having a circular, elliptical, rectangular or square section. The tip or edge of the xe2x80x98pointedxe2x80x99 member should provide a small area of support for the ball or roller so that any significant distortion of the two ends of the valve body will cause the ball or roller to be displaced.
The ball or roller may be housed in an insert member within the valve body. A guide for the ball or roller, e.g. a bore, may be formed in the insert member, which also includes at least one passageway to permit fuel to flow during normal operation through the valve body. The passageway is sized and/or shaped so that a ball which escapes in the event of breakage or distortion of the valve body cannot pass through and jam the shut-off valve. Conveniently, the insert member may be threaded for convenient location and fixing within the valve body.
The pointed member is also supported in or on a second insert member which may also be threaded for easy location within the valve body. In a similar way to the insert member which supports the ball or roller, the second insert member also includes at least one passageway to allow fuel to pass through the valve and which is shaped or sized to prevent a displaced ball or roller from passing through and jamming the non-return valve.
The displacement device may include release means which is sensitive to elevated temperature, whereby in the event of an adjacent fire, the ball or roller is released and the shut-off valve is caused to close.